Method of making a flat composite body with an asymmetric laminar structure

ABSTRACT

A flat composite body with an asymmetric laminar structure generally consisting of a first layer of material, a foam core intermediate layer and a decorative second layer of non-metallic material, wherein a fleece with an epoxy binder is placed between the first and intermediate layers and a fiber matting with an epoxy binder is placed between the intermediate layer and the second layer.

[0001] The invention relates to a flat composite body as a vehicle bodyelement with an asymmetric laminar structure consisting of a first outerlayer of an aluminum material, a steel sheet, or a sintered metal sheet,also consisting of an intermediate layer, in particular a foam core, anda second inner layer of a non-metallic material.

[0002] The invention also relates to a process for manufacture of such aflat composite body.

[0003] A generic composite body and accordingly a process formanufacture of such composite body is known from the essay“Considerations relating to large-series use of sandwich components,their design and configuration, based on the example of the AUDIresearch vehicle hood” in the series of status BMFT [German FederalMinistry of Research and Technology] status reports ‘Development trendsfor motor vehicles and fuels,’ Research Survey 1982, pages 167-177,published by TÜV Rheinland. The essay concerns itself with light-weightconstruction in a sandwich design, using a motor vehicle hood as anexample. Design, configuration, and manufacturing considerationsindicate the possibilities and limits of this light-weight constructionprinciple. Various exemplary embodiments are shown on pages 171 and 172in connection with the laminar design. In one of the embodiment examplesthe cover layers consist of aluminum or laminated sheet metal andplastic. This results in an asymmetrical laminar design. The coreconsists preferably of Structhan (thermoreactive, foamed,fiberglass-reinforced plastic of variable specific gravity). Structhanassumes the function of stress equalization (prevention of warping).

[0004] DE 39 534 C2 describes a process and a support mould formanufacture of plates and platelike articles such as doors, inparticular

[0005] refrigerator doors. An asymmetric laminar design is created inthis instance as well, with a sheet metal covering layer on one side anda sheet plastic covering layer on the other and a hard cellular materialexpanded in situ from a liquid reaction mixture between these twolayers. An effort is made to counter the danger of warping due todifferent thermal expansion coefficients by subjecting the sheet metalcover layer and/or the sheet plastic cover layer before expansion to oneof the preshaping processes which offsets and counteracts the warpingwhich occurs during cooling. The warping that occurs is not subject tocalculation and must be determined empirically.

[0006] For the sake of clarity, reference is made to WO 83/00840 whichdescribes a composite body, in particular a composite plate for theconstruction of ship walls, container walls or the like with adouble-sided rigid outer layer, a one-part or multi-part foam-core andfiber-reinforced intermediate layers made of fiberglass or the likebetween each outer layer and core as well as hardened plastic forconnecting the entire arrangement. Thereby a symmetrical design isachieved in which each outer layer consists of a material with acompressive strength of approximately at least that of high-gradealuminum.

[0007] On this basis the object of the invention is to prepare a flatcomposite body as a vehicle body element with an asymmetrical laminarstructure of low weight accompanied by high dimensional stability andhigh rigidity, along with good paintability.

[0008] The solution claimed for the invention lies in a flat compositematerial asymmetric in structure having the characteristics specified inclaim 1. Claim 7 specifies a process especially well suited formanufacture of such a material. Advantageous configurations anddevelopments of the invention are specified in the relevant subsidiaryclaims.

[0009] The invention is explained in detail with reference to anembodiment of such a flat composite material, an especially well suitedinstance of application of which is a self-contained passenger car bodypart such as a hardtop.

[0010] In the drawings

[0011]FIG. 1 shows a passenger car without hardtop,

[0012]FIG. 2 the same motor vehicle with hardtop installed,

[0013]FIG. 3 the hardtop isolated, and

[0014]FIG. 4 a sectional diagram of the hardtop along lines IV in FIG.3.

[0015]FIG. 1 presents a sectional view of a passenger car 1 with trunklid 2, left and right rear fenders 3, 4, left and right vehicle doors 5,6, and windshield frame 7. A passenger compartment 8 corresponding to aconvertible is open at the top.

[0016] A continuous receiving and fastening mechanism 9 is provided onthe edges of the trunk lid 2 and the fenders 3, 4 facing the passengercompartment 8. A corresponding receiving and fastening mechanism 10extends along the upper, horizontally positioned, section of the frame7. Both receiving and fastening mechanisms 9, 10 perform the function ofreceiving a hardtop 12 as shown in FIG. 2, so that the passengercompartment 8 may now be closed at the top. Hence the hardtop 12 may beinstalled or removed as desired, so that the passenger car 1 may bedriven optionally with the corresponding equipment.

[0017] For the sake of clarity the hardtop 12 is again shown separatelyin FIG. 3, while the laminar structure of this asymmetric flat compositeelement is to be seen in FIG. 4. The outer layer 13 is made of apreformed blank of an aluminum material; in this instance as well usemay be made of sheet steel or a sintered metal, for example. Adjoiningthis outer layer 13 is nonwoven polyester material (fleece) 14 providedwith an expanded epoxy resin bonding agent. An inner layer 15 on thepassenger compartment side is in the form of decorative material next towhich in turn is fiber matting 16 provided with an expanded epoxy resinbonding agent. The cavity is filled with a polyurethane (PU) foam core17; consideration may also be given to use of an EPS core, other lightfoam materials (polypropylene, etc), or a core of blown glass withbonding agent. Inserts 18, for example ones also of a an aluminummaterial, may be provided at suitable points inside the cavity and maybe connected to the outer or inner layer 13, 15 by means of a screwconnection 19.

[0018] The flat composite material, the hardtop 12 shown in theexemplary embodiment, consists preferably of a metal surface, nonwovenpolyester material (fleece) which may be a common commercial productsuch as is used in kitchen vapor filters, a foam core of average density(approximately 20 kg/m³ to approximately 100 kg/m³),

[0019] fiber matting (randomly distributed chopped glass fiber mattingwith a finish preferably suited for epoxy resins, optionally containinga thermoplastic binder for thermal deformation), and a decorativemultilayer foil, preferably with a PUR barrier layer. Suitable asdecorative foil materials in particular are thermoplastic foils with anintegrated barrier layer (intended to prevent foam breakthrough in presscompaction), but also natural products such as leather, for example, ifit withstands a foam pressure of about 1.5 bar without breakthrough.Nonwoven polyester and staple fiber matting are additionally moistenedwith expanding epoxy resin.

[0020] The specific laminar structure is presented below:

[0021] Sheet aluminum (alkaline cleaned); sheet thickness 1.1 mm

[0022] Polyester fleece, 300 g/m²

[0023] PU foam core with sg (specific gravity) approximately 54 kg/m³

[0024] Chopped glass strand fiber mat: 450 g/m²

[0025] Polyurethane decorative fabric: 70 μm foil barrier,

[0026] whereby an expanding matrix system acting as binder, with areactive resin mass (total amount of resin+hardener+propellant) of 1600g/m² (outer) and approx. 1300 g/m² (inner) is further specified asfollows:

[0027] Resin: Araldit® LY 5054 (made by Ciba Spezialitätenchemie AG,Basel)+1% propellant

[0028] Hardener: XB 5003-1® (made by Ciba Spezialitätenchemie AG, Basel)

[0029] Propellant: DY 5054® (made by Ciba Spezialitätenchemie AG, Basel)

[0030] Mixture ratio: 100:20% by weight components,

[0031] whereby it is possible to expand the reactive resin mixture andthe resulting foam does not collapse when the separating agent, based onPAT® 921/A, made by the Würtz Company, is used.

[0032] In theory all liquid epoxy resin systems which can react to ahardener/hardener mixture are suitable as an expanded matrix systemserving as bonding agent. Preference is given for this purpose tobisphenol epoxy resins such as bisphenol-A and bisphenol-A/F epoxidesmodified with stabilizers and thixotropic agents. Also suitable areglycidyl ethers of aliphatic alcohols or polyalkylene glycol, as well

[0033] as solid epoxy resins which may be processed in the liquid statewhen mixed with a liquid epoxy resin; bisphenol-A epoxy resins, forexample, may be employed as solid epoxy resins.

[0034] Theoretically all known liquid hardeners may be used ashardeners, for example, aliphatic, cycloaliphatic amines and theiradducts with epoxides, for example, as well as polyamide amines. Otheradditives which promote hardening, e.g., tertiary amines, may be used inthe mixtures, depending on the epoxy resin systems.

[0035] The fleece to be used in accordance with the invention serves thepurpose of so-called back tension which equalizes stresses resultingfrom asymmetry. Consequently, the fleece must vanish during thehardening process. Examples of fleeces are thermoplastic fleeces, withfleeces made of thermoplastic polyesters being preferred. Theoreticallyall common fibers such as those of glass, carbon, kevlar, and naturalfibers may be used. Glass strand fibers present the advantage that theycan be thoroughly mixed with foam; in theory all fiber glass fabrics andcomplexes may be used.

[0036] The following process is carried out in manufacture of the flatcomposite material (hardtop 12) claimed for the invention.

[0037] First the outer layer 13, such as an aluminum plate, is workedwith a suitable deep-drawing die into the subsequent shape of thehardtop 12 and the edge outlines are then cut (by laser cutting, forexample). The surface of the blank is then subjected to alkalinedegreasing to improve adhesion. The alkaline degreasing consistspreferably of the steps represented by degreasing, rinsing, causticpassivation, rinsing, drying. The process may be continued withcataphoresis priming, optionally in the dipping process (KTL), inaddition to anticorrosive coating such as zinc phosphating.

[0038] The PU foam core 17 provided between the inner and outer layers13, 15 is foamed in a suitable tool before the individual compositelayers are assembled and bonded. The foam blank is then wrapped in fibermatting 16 and fleece 14 and wetted with expanding epoxy resin.

[0039] To bond the individual layers together and accordingly producethe hardtop 12 in a single operation a suitable compression molding dieis used to introduce the preformed outer layer 13 into the die matrix,the inner layer 15 (decorative layer) is stretched over the die stamp,and the foam core 17, positioned opposite the outer layer 13, is alsoinserted into the die matrix. The die mold is then closed by appropriatemovement of the stamp accompanied by pressing of the individual layersand simultaneous hardening.

[0040] Since the expansion relationships among the individual layershave been coordinated with each other, a dimensionally stable compositematerial is obtained. Stability of shape is achieved especially whenepoxy resin is used in that no contraction occurs in the liquid phase asa result of expansion except for the negligible cooling contraction. Thevolume of the foam system must be maintained until jelling takes place.

[0041] Experiments have been conducted which show it to be advantageousif the compressive molding dies are at a temperature of approximately 40to 50° during pressing of the individual components of the flatcomposite material. Good results have been obtained with a pressing timeof around 60 minutes. Other temperatures and pressing times areconceivable. The compressive molding dies should be suitably adjustable.

[0042] The result obtained is a flat composite material possessing theadvantages indicated above, along with good paintability of the metalsurface (outer layer 13).

[0043] It is also possible during the manufacturing process to buildhollow pipes for later cabling in the cavity later filled with PU foamcore. Fastening elements such as bolt-on plates or inserts may also be,used. Nor is the invention restricted to the application (hardtop)indicated in the exemplary embodiment. Application for other vehicleelements, including ones for rail vehicles and for decorative designelements, spherically shaped facade elements, elements for constructionof fairs and exhibitions, and the like, is also conceivable.

[0044] This process may be used in particular wherever a metal surfaceis needed and low component weight is an advantage. Examples are machinebuilding (moving masses), boat building, aircraft, athletic equipment,interior finishing, panels, facades, furniture, etc.

1. A flat composite body, especially a motor vehicle body element with an asymmetric laminar structure consisting of a first layer of metallic material, an intermediate layer, especially a foam core, and a second layer of a non-metallic material, especially a decorative layer, characterized in that a fleece (14) provided with an epoxy binder is introduced between the first layer (13) and an intermediate layer (17) and in that fiber matting (16) provided with epoxy resin binder is introduced between the intermediate layer (17) and the second layer (15).
 2. A flat composite element as specified in claim 1, characterized by use of an aluminum plate as first layer (13), a polyester fleece (14), a polyurethane foam core of medium density between approximately 20 kg/m³ to approximately 100 kg/m³ as intermediate layer (17), and also characterized by use of randomly distributed glass fiber matting (16), and a decorative multilayer foil with barrier foil as second inner layer
 15. 3. A composite element as specified in claim 1, characterized by the following laminar structure: Sheet aluminum (13) alkaline cleaned, optionally also with corrosion proofing and KTL coating; Sheet thickness more or less 1.1 mm; Polyester fleece (14), 300 g/m², Viledon® 15/500 S; “Kapex” ® polyurethane foam core (17) made by Airex/CH, with a sg (specific gravity) of approximately 54 kg/m³ Chopped glass strand fiber mat (16): 450 g/m² Polyurethane decorative fabric (15): 70 μm—foil barrier, whereby an expanding matrix system acting as binder with a reactive resin mass (total amount of resin+hardener+propellant) of approximately 1600 g/m² (external) and approximately 1300 g/m² (internal) is further specified as follows: Resin: Araldit® LY 5054 (made by Ciba Spezialitätenchemie AG, Basel)+1% propellant Hardener: XB 5003-1® (made by Ciba Spezialitätenchemie AG, Basel) Propellant: DY 5054® (made by Ciba Spezialitätenchemie AG, Basel) Mixture ratio: 100:20% by weight components, whereby it is possible to expand the reactive resin mixture and the resulting foam does not collapse when the separating agent, based on PAT 921/A, made by the Würtz Company, is used.
 4. A composite element as specified in claim 2 or 3, characterized by alternative use of an EPS or PP foam core or blown glass with binder as intermediate layer (17).
 5. A composite element as specified in claim 1, wherein inserts (18), empty pipes, reinforcements, or the like connected to the outer or inner layers (13, 15) are mounted in the cavity filled with the intermediate layer (17).
 6. A process for manufacture of a flat composite element (17) as a motor vehicle body element with an asymmetric laminar structure consisting of a first outer layer (13) of an aluminum material, a steel sheet or a sintered metal sheet, also consisting of an intermediate layer (17), a foam core in particular, and also consisting of a second layer of a non-metallic material, according to claim 1, characterized by the following steps: preforming and trimming the first layer (13), foaming the intermediate layer (17), wrapping the foamed intermediate layer (17) in fiber matting (16) and fleece (14) followed by wetting with an expanded epoxy resin, insertion or arrangement of first and second layers (13, 15) into or association with a tool die or die stamp, insertion of the foamed intermediate layer (17) into the machine tool followed by compression molding of the individual layers accompanied by hardening.
 7. The process as specified in claim 6, wherein the surface of the first layer (13) undergoes alkaline degreasing after preforming.
 8. The process as specified in claim 7, wherein the alkaline degreasing consists of the steps degreasing-rinsing-caustic passivation-rinsing-drying.
 9. The process as specified in claim 6, characterized by a temperature during compression molding of about 40 to 50° C. and by a molding time of about 60 minutes. 